Production of aromatic compounds



United States Patent ()fitice Reissued Dec. 16, 1958 PRODUCTION OF AROMATIC COMPOUNDS Lloyd C. Fetterly, Oakland, Calif., assignor to Shell Development Company, New York, N. Y., a corporation of Delaware No Drawing. Original No. 2,819,322, dated January 7,

1958, Serial No. 399,570, December 21, 1953. Application for reissue April 7, 1958, Serial No. 727,015

13 Claims. (Cl. 260668) Matter enclosed in heavy brackets II] appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

This invention relates to the production of methylaromatic compounds, and more particularly to the production of such compounds which contain a further alkyl radical, such as a second methyl radical, such as paraxylene, 2,6-dimethylnaphthalene and durene.

Various methods have been proposed for the preparation of such compounds as the methylbenezene compounds. Thus, it has been proposed to .cloromethylate toluene to chloromethyltoluene (alpha-chloro-xylene) and then to replace the chlorine by hydrogen, to obtain the net result of the substitution of a methyl radical for a nuclear hydrogen atom in a substituted benzene. On the other hand, it has been proposed to alkylate aromatic hydrocarbons in vapor phase with methanol, in the presence of a phosphoric acid catalyst. However, none of the methods previously proposed for the methylation of aromatic compounds has proven to be entirely satisfactory, for one reason or another. The methods heretofore available have failed to provide a simple, effective and economic method for the methylation of a given aromatic compound to form the monomethyl derivative thereof.

It is, therefore, a principal object of the present invention to provide an improved process for the production of methyl-substituted aromatic compounds. A further object is to provide an improved process for the introduction of a methyl radical in substitution for a nuclear hydrogen atom of an aromatic compound. A more spec'ific object of the invention is to provide an elfectiveand economical method for the production of nuclear methyl detailed description of the invention.

Now, in accordance with the present invention, it-has been found that 'diarylmethane (Ar CH compounds (methylenediaryls) ,can be converted into corresponding arylmethane (ArCH compounds and aryl(Ar-H-) compounds by cracking the compounds in admixture with hydrogen with hydrogenation at an elevated temperature and pressure and in contact with a catalyst active for arylmethylene-carbon and aryl-carbon linkage cleavage and having hydrogenation activity. In general the high melting compounds of the group VIVIII metals having an atomic number of at least 24 are suitable, particularly the variable valence metals. A particularly suitable catalyst for this purpose is, for example, a tungsten-nickelsulfide catalyst such as is utilized commercially for the dehydrogenation of methylcyclohexane'to toluene. The dehydrogenating metal sulfides are a preferred class of catalysts for the process, particularly the group VI metal sulfides, as, for example, the sulfides of tungsten, molybdenum and chromium, and the sulfides of metals of atomic number from 25 to 28, especially nickel sulfide. Composites of a metal sulfide from each of these groups are especially preferred. Corresponding oxides and ,composites thereof .are also suitable catalysts for the present purpose, as well as composites of oxides and sulfides.

The diaryl methane compounds which are to be cracked in accordance with the invention, in general are preparable by the alkylation of the corresponding aryl compound with formaldehyde. For example, it is known to prepare diphenylmethane, ditolylmethane (mixture of isomers) and dixylylmethane, by reacting the corresponding benzene compound with formaldehyde in the presence of an acidic catalyst, such as sulfuric acid. Similarly, other compounds can be prepared, such as di betanaphthylmethane from naphthalene, di-beta-5,6,7,8-tetrahydr-onaphthylmethane from tetralin, di-2,4,5-trimethylphenylmethane from pseudocumene, bis-(2,4-dimeth'ylphenyl)methane from meta-xylene, 'bis-(beta-G-methylnaphthyl)methane and bis-(beta-7-methylnaphthyl)methane from beta-methylnaphthalene.

Other diarylmethane compounds to be converted by the present invention can be made bythe indicated alkyla tion with formaldehyde, as will be understood. In general, the diarylmethane compound ispref'erably volatile at the conditions of thereaction to beutilized.

As already indicated, the diarylmethane compounds, which may be represented by the formula ArCH --Ar, wherein the Ar" groups are usually the same aryl radicals having the same empirical formulas, although they may be different position isomers and can be even different types of radicals, are cracked in the practice of the invention, with hydrogenation, to yield two substances, one an arylmethane (Ar-CH and the other a emesponding aryl compound, ArH The gross reaction 'can be represented by the equation Thus, the net result of the reaction is the cleavage of a CC bond between the methylene (C H carbon and a carbon atom of one of the aromatic rings and a saturation with hydrogen of the two bond fragments. The kinetics or methanism whereby this result is eifected is not clear, although it is considered to involve more than .a mere carbon-to-carbon cleavage 'and hydrogenation. In

These diarylmethane (arylmethyldiarylmethane) compounds are also cracked in the same manner and under similar conditions to yield two molecules of methyl-v aromatics and one molecule of the original aromatic. Even higher polymers are cracked similarly. It is contempl'ated, in the present invention to crack the mixture of dimer, trimer and other polymer which may be obtained by the alkylation, the polymer preferably being kept toa minimum.

An examination of the equations for the reactions for (1) the formation of the dimer and (2) the cracking of the dimer; namely,

shows that the overall result is the conversion of one. mole of aromatic compound (ArI-I) to one mole of. corresponding methylaromatic or arylmethane (ArCn for each two moles of initial aromatic feed. However,

, one mole of the aromatic compound is produced in the second stage, which can be recycled to the first stage. Thus, the theoretical net consumption of aromatics is one mole for each mole of desired methylarornatic pro duced. Therefore, a preferred method of practicing the invention comprises: (1) alkylating the aromatic com.- pound, such as toluene, with formaldehyde to produce. the diarylmethane (ditolylmethane), which will normally be a mixture of isomers (p-p, o-p, m-p) predominat-- ing in the p-p isomer; (2) cracking the diarylmethane product, either the total alkylate, or the portion from which the higher polymers have been removed, as by distillation, to yield a mixture of isomeric methylaromatic compounds (xylenes, predominantly the para-isomer) and of corresponding aromatic compound (toluene); (3) separating the produced methylaromatics from regenerated aromatic as by distillation whereby the regenerated aromatic (toluene) is recovered as overhead distillate; (4) and recycling the regenerated aromatic to the alkylation step, When the alkylation results in an appre'ciable proportion of polymer, for example, tetramer .and'higher, it is preferable to separate the polymer as by distillation, and to crack the fractions separately under somewhat different conditions, because of the greater tendency of the higher boiling materials to deactivate the catalyst under the same conditions. The cracked streams are then combined and processed together.

In thepreparation of xylenes, the separated xylene isomer mixture can then be de-orthoized, as by distillation, and the para-xylene readily recovered in high yield and substantially pure.

The invention is of particular utility for the production of durene, wherein pseudocumene is alkylated and the 'dipseudocumylrnethane is hydrocracked to durene and pseudocumene. The pseudocumene can be prepared from meta-xylene by alkylation with formaldehyde and hydrocracking the alkylate, di-metaxylylmethane (d1- (2,4-dimethylphenyl) methane), by the process of this m- I o n F vention. Pseudocumene is also readily available in certain refinery streams, such as bottoms lay-product streams from the production of aromatics, including xylenes, by various hydroforming operations. Thus, an illustrat ve refinery xylene bottoms by-product having a precision boiling range of about 150 C. to 205 C., hasthe composition as shown in Table I, with the boiling points being given for the individual components.

By fractional distillation, the three trimethylbenzenes are easily concentrated further in a heart cut. By mak ng the fractionation sufllciently sharp, a large proportion of j the hemimellitine is also readily rejected from the pseudocumene concentrate, so that the concentrate is comprised essentially of pseudocumene and mesitylene with .a very small proportion of hemimellitine and only a small proportion, not over about l2%, of methyl ethyl benzene. This pscudocumene concentrate is then alkylated and the resulting alkylate is hydrocracked in accordance with the invention to yield durene. The pseudocumene :alkylates primarily to the bis-(2,4,S-trimethylphenyl)- :methane, thus giving by hydrocracking primarily durene as the tetramethyl benzene compound, one molecule of pseudocumene being regenerated. A minor portion of the pseudocumene goes to bis-(2,3,5-trimethylpheny1)-meth- .ane, which on hydrocracking yields isodurene and pseudocurnene. And a further minor portion alliylates to the mixed C -isomer, 2,2',3,4'5,5-hexamethyldiphenylmethane, some of which on hydrocracking yields durene, in addition to regenerated pseudocumene, while the other yields isodurene, depending on which aromatic ring is cleaved from the methylene carbon atom. The .mesitylene alkylates essentially to only one dimer, bis- (2,4,5-trimethylphenyl)rnethane, which hydrocracks to .isodurene and mesitylene. The hemimellitine present :alkylates to three dimers, which hydrocrack to regencrate hemimellitine and a mixture of isodurene and 'prehnitene. The regenerated trime'thylbenzenes are .readily separated by distillation and recycled to the alkylation, where desired. The durene (M. P. 7980 C.) is readily crystallized in good yield from the isodurene (M. P. 24 C.) and prehnitene (M. P. 4 C.) in the separated fraction.

The cracking-hydrogenation of the diarylmethanes is readily effected by passing a suitable mixture of the feed alkylate and hydrogen over the heated catalyst at a sufficiently elevated temperature and under a suitable superatmospheric pressure. A broad range of mole ratios of hydrogen to alkylate can be utilized, in general a ratio of from about 1 to about 20 being suitable, with a ratio of from about 2 to 10, and particularly about 4 or 5, giving especially satisfactory results. The temperature in the reaction zone is advantageously maintained at about 400-450 C. with a pressure of about 250-275 p. s. i. g., although higher and lower temperatures such as 500 C. and,350 C., respectively, are effective with pressures which may be from about p. s. i. g. to about 500 p. s. i. g., or even lower or higher. A contact time corresponding to a liquid hourly space velocity (LHSV) of about 5 has been found to be particularly effective although the space velocity may range suitably from a value as low as about l-LHSV to as high as about 20- LHSV. It will be understood that the optimum set of conditions will depend on a number of variable factors, including the particular catalyst employed, the particular alkylate feed and whether it is a single compound or a mixture of polymers, the particular apparatus employed, and the like.

The cracking-hydrogenation of the diarylrnethanes is slightly exothermic in character (AI-i=ca. 18,000 B. t. u./ lb. mol H reacted) although usually of such a small amount that no particular problem of heat removal is presented. The feed mixture of alkylate and hydrogen is normally preheated to about the reaction temperature prior to contacting it with the catalyst.

The reaction can be suitably carried out by passing the alkylate and hydrogen over or through a fixed bed or mass of the catalyst in particulate form, such as a bed of pellets or a packed section thereof in a confined reaction zone. On the other hand, the reaction can be readily carried out by passing the preheated mixture of alkylate and hydrogen through a fluidized catalyst mass, and the temperature of the catalyst mass can be readily controlled byany suitable means, such as by providing heat transfer tubes disposed in the catalyst zone or by ey1in :a'- portion ofdie catalyst to" an externa heat excliangerand back to the'reaction" zone.

'Tlieifollowing' detailed description of illustrative examplesi'off'the' practice of the invention are given for the purpose of. a better understanding, thei'eof'and are not to be considered aslimitative thereon.

EXAMPLE I in.a wcightratiobf. 62:12:26, respectively. The yieldof mixedalleylatei was 9.9-1.'O0.%', Jbased ontoluene converted and '95-100922', based upon the; formaldehyde; Since the sulfuric. acid isrelatively dilute, little if anysulfonation' of 'toluene or produetoccurre'd' and acidconsumption was-negligible.

The dimer, trimer and higher polymer arerea'dily. separable lay-distillation; Thedimer (DTM') fraction contained'aniis'orner distribution of approximately 60% p-p', 35% o-p" and 5% m-pfiasdetermined by infraredanalyses and'from analyses ofthe products from subsequent cracking in accordance with. the invention.

- (8) Alkylation of toluene-Toluene was alkylated Withformaldehyde in the presenceof a sulfuric acid, methanol, water mixture andv summarized in-the following tabulation: 1

Temperature 90---1'()0' C.

Pressure; Atmospheric;

Catalyst: composition, percentaw; H S0 -63.-

CH OH'-20.'- Product distribution, percent wz. Dimer-81.

T-rimerl4 4.-

Higher molwt. 4:6.

Yield tbased onto1uene 96.9 m.

Yield: based: on' formaldehyde 96.4% m.-

Methanol recovery 57+percent m. as CH OH.

e 41% m asCH3OHH' SO reactionproduct.

66.7% w. as titratable acid.

Sulfuricv acidi recovery--- 33.3%- w. as CH OH-- B28041 Reaction time; 20 minutes. Conversion of toluene; 45%: w.'.

dimerztrimenpolymer wasobtained at a 41% alkylate level and a reaction'time of minutes when using a 1:1.1 volume ratio of96% H 50 and'methan'ol as catalyst;

(D) Alkylation Of'Xyl6I18S.ThB three isomeric xylen'es,= 0-, -mandp-, were separately alkylated with formaldehyde; using sulfuric acid as catalyst in aqueous methanol solvent. The product 1 distributions in the alkylates of the threetcasesare-tabuia-tedin Table II.

Xylene Alkylate d o-wle'nn nil-xylene p-xylene (E) Alkylation of pseudocumene.Pseudocumene (1,2,4-trimethylbenzene) was alkylated with to'rmaldehyde in the presence of aqueous methanolic sulfuric acid as catalyst, at a temperature of- 5080 C. and a reaction time of 20 minutes. .A yield of 99%, based onconverted pseudocumene, was obtained,. of a product which, when recrystallized had the following properties: melting point, 70-72" C.; mol. wt=ca. 250; molecular formula- C H From analyses, including the fact that the tetramethylbenzeneproduct obtainedby cracking it by the process of this invention was predominatelyduren'e, this product was considered to be predominately bis-(2,4,5- trimethylphenyl)methane. About 8% by weight of isomeric material: was obtained, an approximately equal mixture of the isomers; -bis-(2,3,5-trimethylphenyl methane and 2,2 ,3',4,5 ,5 -hexainethyldiphenylmethane.

EXAMPLE II (A) Ditolylni'ethanewas hydrocracked in admixture with hydrogen by assing itover a tungsten-nickel-sulfide p'elleted catalyst a't-400 (2., 260 p. s.- i. g. pressure,

- 1 LHSVof 5' and'a-hydroge'n to-ditoly-lmet-hanemole ratio of 4. The feedwas50 to 7-5% convertedtoother proclucts with 100% yield. The hydrocracking was carried out by vaporizing the ditolylmethane, mixing it with the hydrogen, preheating the mixture to about the reaction temperature, and passing the mixture over the catalyst packed in a steel reaction tube, while. maintaining the temperature at the selected value. Thepr'oduc't was fractionatedby distillation withthe recovery of 61% w. low boiling fraction which contained 53% xylene and 46% toluene and 39% w. higher boiling components comprising predominantly dimer and trimer (88:12 ratio). The xylene'product isomer distribution was about p-xylene, 22% ortho-Xylene and 3% m-xylene.

(B) A portion of the total alkylate of -EXample'I-A was hydrocracked under'the same conditions as in II-A. In this case the total yield of low boiling product was 32% by, weight, containing 63% w. xylene and'37% "w, toluene, and 68% higher boiling material. The fact that the xylene content was greater than the toluene content is the result of cracking ofialkylates' higher than dimer. Thus, a trimer yields two mols of xylene per mol of toluene.

EXAMPLE III The recrystallized bis-(2,4,5-trimethylphenyl)methane product from Example I-E, and having amelting pointof 7072 C. was-hydrocracked over a W/Ni/S catalyst at about 450 C., apressureofabout 600 p. s. i. g. anda mole ratio of hydrogen to alkylate of 10 to 1, respectively. Durene was recovered from the product in a yield of above based on the pseudocumene alkylate converted, ata-conversion level of about 91%. The other product was'essentially all pseudocumene, with a very small proportion of isodurene and prehnitene being present.

EXAIVLPLE IV The remainder of the pseudocumene alkylate from Example 'IE wa's hydrocracked similar to Example III. The product from the cracking was predominantly durene with minor proportions of isodurene and prehnitene, butlarg'er proportions than in Example III, in addition to pseudocumene.

EXAMPLE V When a 162 C. to 173 C. distillate fraction from a refinery xylene bottoms product, as described in Table I, and containing about 90% pseudocumene is alkylated with formaldehyde in the presence of sulfuric acid-.

aqueous methanol as catalyst, an alkylate product comprising essentially dimers is readily obtained. The hydrocracking of this alkylate over a W/ Ni/ S catalyst under a pressure of about 600 p. s. i. g. and at a temperature of about 450 C., with a mole ratio hydrogen/alkylate of about 5, yields a mixture composed essentially of triand tetra-methylbenzene compounds. The trimethylbenzenes are readily separated by distillation as distillate for recycle to alkylation, to give a residual mixture composed essentially of durene, isodurene and prehnitene.

The durene is readily recovered in a yield of about 83 mol percent, based on trimethylbenzenes consumed.

About 17 mol percent of a mixture of isodurene and prehnitene are recovered, being about 10% isodurene and 7% prehnitene. The prehnitene (M. P.=4 C.) and isodurene (M. P.=24 C.) are separable by fractional crystallization- EXAMPLE v1 When the mixture of isodurene, prehnitene and unsep-.

arated durene from Example V is alkylated with formaldehyde and alkylate, bis-(2,3,4,6-tetramethylphenyl)methane is obtained which has a melting point above 150 C. and is slightly soluble in toluene. When this alkylate is hydrocracked similar to the process of Example V, pentamethylbenzene is obtained as product admixed with a mixture of isodurene, prehnitene and durene. The pentamethylbenzene (M. P. 53 C.) is readily recovered by crystallization and filtration or centrifugation.

EXAMPLE VIII When di-p-tolylmethane is hydrocracked under conditions similar to those of Example II, but the catalyst is pelleted molybdenum disulfide instead of the tungstennickel-sulfide catalyst, similar results are obtained but at a slightly difierent conversion.

EXAMPLE IX When Example II is repeated except that the catalyst charged to the reactor is a mixture of nickel and tungsten oxides (nickel tungstate) and a small amount of hydrogen sulfide is incorporated in the feed stream (about 1 mol percent), the ditolylmethane is hydrocracked in essentially the same manner as in Example II.

EXAMPLE X When Example II is repeated except that the catalyst employed is a composited cobalt oxide-molybdenum oxide (Co/Mo/O) catalyst, the di-p-tolylmethane is readily converted in similar proportions to paraxylene and toulene.

The invention claimed is:

1. A process for the preparation of a polymethylbenzene having from three to five methyl groups which cornprises hydrocracking a diarylmethane in which each aryl group is a methyl substituted phenyl group having from two to four methyl group substituents at an elevated temperature and a pressure from about to about 600 lbs/sq. in., gauge, in the presence of from about one to about twenty moles of hydrogen per mole of diarylmethane and a high melting inorganic compound selected from the group consisting of oxides, sulfides and composites thereof of group VI and VIII metals having atomic numbers of at least 24, as catalyst.

2. A process in accordance with claim 1, wherein the temperature is from about 350 to about 500 C.

3. A process in accordance with claim 1, wherein the polymethylbenzene is pseudocumene and the diarylmethane is di-(2,4-dimethylphenyl)methane.

4. A process for the preparation of durene which comprises hydrocracking bis-(2,4,5-trimethylphenyl)methane at an elevated temperature and a pressure from about 100 to about 600 lbs/sq. in., gauge, in the presence of from about one to about twenty moles of hydrogen per mole of bis-(2,4,5-trimethylphenyl)methane and a high melting inorganic compound selected from the group consisting of oxides, sulfides and composites thereof of group VI and VIII metals having atomic numbers of at least 24, as catalyst.

5. A process for the preparation of a polymethylbenzene having from three to five methyl groups which comprises hydrocracking a diarylmethane in which each aryl group is a methyl substituted phenyl group having from two of four methyl group substituents at a temperature of from about 350 to about 500 C. and at a pressure from about 100 to about 600 lbs/sq. in., gauge in the presence of from one to twenty moles of hydrogen per mole of diarylmethane and a tu'ngsten-nickel-sulfide catalyst.

6. A process for the preparation of pseudocumene which comprises hydrocracking di-(2,4-dimethylphenyl) methane at an elevated temperature and a pressure from about 100 to about 600 lbs/sq. in., gauge, in the presence of from about oneto about twenty moles of hydrogen per mole of the methane compound and a tungstennickel-sulfide catalyst.

7. A process for the preparation of durene which comprises hydrocracking bis-(2,4,5-trimethylphenyl)methane at an elevated temperature and a pressure from about 100 to about 600 lbs/sq. in., gauge, in the presence of from about one to about twenty moles of hydrogen per mole of the methane compound and a tungsten-nickel-sulfide catalyst.

8. A process for the preparation of pentamethylbenzene which comprises hydrocracking bis-(2,3,4,5tetramethylphenyl)methane at an elevated temperature and a pressure from about 100 to about 600 lbs/sq. in., gauge, in the presence of from about one to about twenty moles of hydrogen per mole of the methane compound and a tungsten-nickel-sulfide catalyst.

9. A process for the preparation of a polymethylbenzene having from three to five methyl groups which comprises hydrocracking a diarylmethane in which each aryl group is a methyl substituted phenyl group having from two to four methyl group substituents at a temperature of from about 350 to about 500 C. and at a pressure from about 100 to about 6.00 lbs/sq. in., gauge in the presence of from one to twenty moles of hydrogen per mole of diarylmethane and a cobalt-molybdenum-oxide catalyst.

10. A process for the preparation of a polymethylbenzene having from three to five methyl groups which comprises hydrocracking a diarylmethane in which each aryl group is a methyl substituted phenyl group having from two to four methyl group substituents at an elevated temperature and a pressure of at least about 100 lbs/sq. in., gauge, suitable for hydrocracking, in the presence of from about one to about twenty moles of hydrogen per mole of diarylmethane and a high melting inorganic compound selected from the group consisting of oxides, sulfides and composites thereof of group VI and VIII metals having atomic numbers of at least 24, as catalyst.

11. A process in accordance with claim 10, wherein the temperature is from about 350 to about 500 C.

12. A process in accordance with claim 10, wherein the polymethylbenzene is pseudocumene and the diarylmethane is di(2,4-dimethylphenyl)methane.

13. A process for the preparation of durene which comprises hydrocracking bis (2,4,5 trimethylphenyl)- methane at an elevated temperature and a pressure of at least about 100 Ibs ./sq. in., gauge, suitable for hydrocracking, in the presence of from about one to about twenty moles of hydrogen per mole of bis-(2,4,5-trimethylphenyDrnethane and a high melting inorganic compound selected from the group consisting of oxides, sulfides and composites thereof of group VI and VIII metals having atomic numbers of at least 24, as catalyst.

References Cited in the file of this patent or the original patent UNITED STATES PATENTS OTHER REFERENCES Globus et a1.: Journal of Applied Chemistry (U. S. S.

15 12. vol 17, pp. 623-628 1944 

